Holden's first Tube station series was for the southern extension of the Northern line from Clapham Common to Morden, opened in 1926. Initially, Stanley Heaps, head of the Underground's Architects Office had created new designs for the stations but following concerns raised by Pick, Holden took over the project. He developed a standard 'folding screen' entrance design that could be adapted to each site, whether it was freestanding or inserted into an existing building. The facades were in white Portland stone with large glazed areas and prominent Underground roundels. Floodlighting and bright internal illumination made each station stand out like a beacon on a dark street. Around the same time, both Bond Street and St Paul's stations were rebuilt to handle the increase in passenger traffic and Holden used the same design elements as he had developed for the Morden extension.